Isospin mixing in the 60Zn nucleus

An experimental study of the isospin mixing for the 60Zn nucleus was made by measuring the γ-decay from the Giant Dipole Resonance. Two compound nuclei, 60Zn and 62Zn, were populated at two different excitation energies, E∗ = 47 MeV and E∗ = 58 MeV, using the fusion evaporation reactions 32S +28 Si, at the bombarding energy of 86 MeV and 110 MeV, and 32S +30 Si, at 75 MeV and 98 MeV. The 62Zn nucleus was used as a reference. In the experiment, performed at the LNL-INFN laboratory, the γ-rays were measured with the GALILEO detection system in which large-volume LaBr3(Ce) detectors were added to the HPGe detectors. The Coulomb spreading width was obtained from the comparison of the two reactions. The isospin-mixing coefficient at zero temperature, of the order of 2.5%, was deduced and the measured value agrees with that from mass and beta-decay measurements and with theory. The isospin-symmetry-breaking correction δc used for the Fermi super-allowed transitions was also extracted from the value of the isospin impurity.